DISSOLUTION CHARACTERISTICS OF WEATHERED PETROLEUM DEPOSITS FROM THE 2010 DEEPWATER HORIZON BLOWOUT: AN EXPERIMENTAL STUDY

On the 20^th of April, 2010, the Deepwater Horizon petroleum rig in the Gulf of Mexico exploded, resulting in the release of an estimated 4.9 million barrels of crude oil. This affected the aquatic ecosystem in the Gulf of Mexico, and the persistence of hydrocarbons along the Gulf Shore remains a problem. Little research has been conducted on the long-term fate of beach-ridden oil from this particular event, and there is uncertainty of the timing and mode of depletion of these hydrocarbon contaminants.

A novel project has been launched to investigate the role of physical geometry on the biodegradation of coastal petroleum deposits, and a sub-study is presented here which aims to characterize the dissolution of these deposits. Dissolution is a critical factor in the biodegradation of non-aqueous phase liquids (NAPLs), and a transfer rate coefficient between the oil and aqueous phase can be used as a parameter in depletion modeling. The complex composition of the oil calls for direct assessment of field samples, and a laboratory procedure was developed to observe dissolution under abiotic conditions.

The procedure involves crafting spherical tar balls from sampled deposits and submerging them in a static setting with artificial saltwater media. Unless equilibrium has been reached, varying the total time of submergence will affect the amount of hydrocarbons that partition to the aqueous phase. Analysis using gas chromatography (GC-FID) and by measuring total organic carbon (TOC) will provide dissolution rates, allowing the calculation of a transfer-rate coefficient. Results will also indicate the effectiveness of this procedure for assessing the dissolution of petroleum products as well as other NAPLs.